I've always been after a two-step approach, which sort of precludes a middle-range stone. Soft Ark for bevels and translucent or black Ark for the finish. One side of the soft Ark can be smoothed, taking it towards the middle, and one side of the translucent or black Ark can be kept freshly lapped, again, taking it towards the middle.
Like Brooksie, I know that what I would ultimately want from a middle-range stone is a stone that can do everything. Two-sided hard or true hard Arkansas perhaps? Lily white Washita? Or maybe a BBW? Don't think a Hindostan would really fit in with a Jnat progression.
Speaking of arks....the bottom one is the one that will get me from the grey one to the SB on the right. Slowly, but surely.